1. Technical Field of the Invention
The present invention relates generally to the field of oscillatory motors and devices incorporating them, such as portable and hand-held oscillating devices for application as toothbrushes, oral hygiene devices, personal healthcare devices, and the like.
2. Brief Description of Related Art
The use of handheld oscillating devices for personal healthcare and oral hygiene applications such as power toothbrushes, and the like, has increased significantly. Many power toothbrushes employ a motor, generally located in the toothbrush handle, to vibrate or oscillate a brush head and bristle tufts located on a brush head. Other types of personal care and hygiene devices, portable tools, and the like also employ a motor to vibrate or oscillate a component or an accessory. The motors in these devices may be powered, for example, by connection to an electrical power source, by battery power, or by alternative power sources, such as solar or other renewable power sources. Many portable devices utilize rechargeable batteries.
Various types of drive motors may be used to produce oscillation of a component or an accessory or an end effector at “sonic” frequencies below about 1 MHz. A stepper motor may be used to provide oscillating rotary motion of a motor drive shaft that may be coupled to an end effector such as a toothbrush head. Stepper motors are generally controllable to provide precise manipulation of the amplitude of oscillation. Wobble weight motors, conventional rotary motors, gear motors and piezoelectric motors or actuators may alternatively be used as drive motors for producing oscillations at sonic frequencies.
Limited angle torque actuators operate on the principal that a force, or torque, is exerted on a current carrying conductor placed in a magnetic field. The force is proportional to the direction and magnitude of the current and the flux density field. When a permanent magnet flux density field is fixed, the direction of rotation depends on the polarity of the input current, and the amount of torque produced is directly proportional to the magnitude of the input current. Limited angle torque motors typically incorporate a rotor comprising field magnets and a stator supporting armature windings that are wound single phase, unlike conventional brushless motors, which eliminates the need for commutation circuitry. Armature windings may be embedded in slots provided around the inner periphery of a laminated stator or, alternatively, the armature may be toroidally wound on a slotless stator. Limited angle torque actuators are generally used as positioners for operating servovalves, mirrors, antennaes, and other devices that require rotation through relatively small angles.
Motors producing oscillatory motion for use in personal care devices, such as oral hygiene devices and toothbrushes, typically have relatively high mass and inertia drive requirements and typically require higher torque capability than many otherwise suitable motors provide. In addition, the (small) size, (low) weight and (low) noise requirements for motors used in personal care devices are difficult to satisfy. Oscillatory motors of the present invention employing limited angle torque drivers are designed to satisfy these requirements.